1. Field of the Invention
The present invention relates to an image pickup apparatus that detects a focus state of an image capturing optical system by using output from an image sensor for photoelectrically converting an object image.
2. Description of the Related Art
Such an image pickup apparatus photoelectrically converts, by plural focus detecting pixels provided in the image sensor, paired object images formed by light fluxes passing through mutually different two areas (hereinafter referred to as “two pupil areas”) in an exit pupil of the image capturing optical system to produce paired image signals from the focus detecting pixels. The image pickup apparatus performs correlation calculation on the paired image signals to calculate a phase difference, which is a relative positional difference amount (image displacement amount), between the paired image signals, and then calculates a defocus amount corresponding to a focus state of the image capturing optical system. Such a focus detection method is referred to as “an image sensor phase difference detection method”.
Japanese Patent Laid-Open Nos. 2001-083407 and 2001-250931 disclose image pickup apparatuses each of which is provided with an image sensor whose each focus detecting pixel includes one microlens having a light collection effect and two divided photodiodes (each hereinafter abbreviated to as “PD”) respectively receiving light fluxes from two respective pupil areas. Providing a plurality of such focus detecting pixels in the image sensor makes it possible to produce the above-mentioned paired image signals.
Moreover, Japanese Patent No. 3592147 and Japanese Patent Laid-Open No. 2010-152161 disclose image pickup apparatuses each of which is provided with an image sensor that includes two focus detecting pixel groups in which apertures of wiring layers formed on a light entrance side further than PDs are shifted with respect to pixel centers in mutually different directions. Providing such two focus detecting pixel groups receiving light fluxes from two pupil areas makes it possible to produce the paired image signals.
In such an image sensor phase difference detection method, it is desirable that each image signal be obtained from a focus detection area provided in the image sensor as a two-dimensional pixel area including plural pixel lines and plural pixel columns. This is because a focus detection area including only one pixel line is too narrow to perform good focus detection. Thus, the image pickup apparatus disclosed in Japanese Patent Laid-Open No. 2010-152161 projects outputs of plural pixels included in each of pixel lines in a direction in which the pixel lines extend, and thereby produces an output of each pixel line.
Then, arranging the outputs of the respective pixel lines in a direction in which pixel columns extend enables production of a one-dimensional image signal from the two-dimensional focus detection area. Furthermore, Japanese Patent Laid-Open No. 2010-152161 discloses a method that produces paired image signals for each pixel line, calculates a phase difference (image displacement amount) of the paired image signals and then adds the image displacement amounts calculated for the plural pixel lines to calculate an image displacement amount for the two-dimensional focus detection area.
However, the first one of the image signal producing methods disclosed in Japanese Patent Laid-Open No. 2010-152161 compresses the output of the two-dimensionally arranged pixels into a one-dimensional output, which deteriorates focus detection performance for a specific object such as a transverse line. On the other hand, the second method disclosed therein requires calculation of an image displacement amount for each pixel line, which ensures a certain degree of focus detection performance, but requires a long calculation time.